Structural organization of Great Plains stream fish assemblages:Implications for sampling and conservation

by

Jesse Robert Fischer

B.S., University of Nebraska-Lincoln, 2004

ABSTRACT

We investigated stream fish assemblages in Nebraska and Kansas to determine
the effects of habitat and sampling methodologies on the community structure
and abundance of prairie stream fishes of the Great Plains. We intensively
sampled four mid-sized (9.9 m to 28.9 m wide), wadable streams to determine
the sampling effort needed to assess the status and trends of fish communities.
The number of reaches (<1 km) required to estimate segment (20-30 km) species
richness decreased with increased reach length (10, 20, 40, or 60 mean stream
width [MSW]) whereas total sampling effort decreased with more and shorter reaches.
Only after all 10 reaches was total species richness obtained with 40 to 60 MSW.
The number of reaches needed to detect 50% changes in fish relative abundance
at 0.8 statistical power was 99 (range 7-630) and decreased with increased reach
length. A greater number of reaches was needed to detect 90% of species richness
and 25% changes in relative abundance when community similarity and habitat
heterogeneity was lower. Our results suggest homogenous stream segments
require more reaches to characterize fish community structure and monitor
trends in fish abundance and a greater number of shorter reaches may be better
than fewer longer (e.g. 40 or larger MSW) reaches. Effects of local environmental
influences on the structure of fish assemblages were evaluated from 159 sites
in two regions of the Great Plains with limited anthropogenic disturbance. These
least disturbed regions offered an opportunity to evaluate the structure and
natural variation of streams and fish assemblages within the Great Plains.
We used canonical correspondence analyses to determine the influence of
environmental conditions on species abundances, species occurrences, and
assemblage characteristics. Analysis of regions separately indicated that
similar environmental factors structured streams and fish assemblages, despite
differences in environmental conditions and species composition between regions.
Variance in fish abundance and assemblage characteristic data from both regions
was best explained by metrics of stream size and habitat features linked with
stream size (width, depth, conductivity, instream cover). Our results provide
a framework and reference for least disturbed conditions and assemblage structure
in North American prairie streams.